The present invention relates to a semiconductor light-emitting device to be used for transmission (in particular, for IEEE 1394), display and the like.
In recent years, semiconductor light-emitting devices have been widely used for optical communications, information display panels and the like. These semiconductor light-emitting devices, for which high luminous efficiency and besides, for optical communications use, high response speed are of importance, have been vigorously developed in these years.
Recently, plastic optical fibers have begun to be used for communications of shorter distances. Since these plastic optical fibers have low loss at a wavelength region of 650 nm, there have been developed fast response LEDs (Light-Emitting Diodes) having, as a light-emitting layer, an AlGaInP based semiconductor material capable of high-efficiency light emission at this wavelength region.
On the other hand, as one of the means for improving the response and luminous efficiency of normal plane emission type LEDs, it has been practiced to fabricate the light-emitting layer into a quantum well structure. Further, as a means for improving the light takeout efficiency, it has been practiced to provide a DBR (Distributed Bragg Reflector) having high reflectance between the light-emitting layer and a GaAs substrate.
However, in the plane emission type LED with the DBR provided under the light-emitting layer, given a light-emitting layer which is a quantum well active layer, the light-emitting layer is so thin as about 10 nm that light reflected from the DBR would not be well absorbed by the light-emitting layer but be radiated outside the LED. As a result, the characteristic of the DBR that the wavelength of perpendicularly reflected light is longer than the wavelength of obliquely reflected light is reflected on the LED, causing the emission wavelength of the LED to have a radiation angle dependence, which is generally about 0.2-0.3 nm/deg. However, even such a level of radiation angle dependence, with the LED used for display, would result in a problem that color changes occur depending on the angle of view.
With the LED used as a light source for communications, when the LED chip is fabricated so as to have a light-emission wavelength peak at, for example, the wavelength region of 650 nm at which plastic optical fibers connected perpendicularly have low loss, then there would occur a problem that obliquely directed outgoing light have a peak wavelength shorter than 650 nm so as to be unusable.